The present invention is directed generally to electronic musical instruments, and more particularly to the production of pitch variation effects, such as celeste effects and vibrato effects, by controlled detuning of the tone generating circuits of the instrument.
Electronic musical instruments utilizing digital circuitry and digital techniques to produce musical sounds are generally well known in the art. Among the properties of music reproduced by such instruments are acoustically pleasing effects resulting from variations in the frequency of a tone about a given nominal frequency, or the playing of a tone detuned slightly in frequency with respect to another simultaneously sounded tone. In the former instance, the name "vibrato" is normally applied to the periodic frequency modulation of the pitch of a musical tone during the playing thereof. In the latter case, when two tones of nominally the same fundamental frequency are played in unison, a slight detuning or variation of the pitch of one of these tones produces "beats" which, when they occur at certain frequencies, produce a pleasing effect generally known as "celeste".
Many prior art electronic musical instruments have provided circuitry for varying the pitch of tones in a suitable fashion to produce either celeste or vibrato effects. However, several problems have been encountered in efficiently and inexpensively providing circuitry for producing such effects in conjunction with digital electronic instruments. In such digital electronic instruments the tone generating circuits generally are provided in an all-digital format, wherein a relatively high, radio frequency is generated, and divider circuits having suitable divider ratios are utilized to provide the 12 top tones of the instrument. Thereafter, conventional divide-by-two digital circuits are utilized to provide the corresponding tones in each lower octave of the instrument.
Accordingly, in order to produce a celeste effect in such instruments, it is first necessary to have at least two tone generators assigned to the production of the same note, so that one may be "detuned" or have its pitch varied somewhat relative to the other. However, in digital organs of the type just described, if the celeste-producing circuitry is tuned so as to accomplish a relatively pleasing celeste effect in the lowest octave, for example, one and one-half beats per second, it follows that the number of beats per second produced will double in each succeeding higher octave. A typical instrument has a four or five octave performance range. Consequently, in the fourth and fifth highest octaves of such instruments, conventional celeste circuitry will produce 12 beats per second and 24 beats per second, respectively. Generally speaking, however, a celeste effect in excess of six beats per second is not considered musically pleasing.
Moreover, it has heretofore been the practice to produce celeste effect in such digital instruments by providing two complete sets of master or top octave frequencies and detuning one set from the other. Accordingly, with the ensuing divide-by-two ratios of lower octaves, a choice must be made between producing a suitable celeste effect (six beats per second or less) only in the higher octaves while producing no effect whatsoever in the lower octaves, or conversely, producing a suitable celeste effect in the lower octaves only.
However, novel digital integrated circuit tone generator components are shown and described in the co-pending applications of Schwartz et al, Ser. No. 917,313, now U.S. Pat. No. 4,203,337 and Schwartz et al, Ser. No. 917,314, now U.S. Pat. No. 4,256,002 both filed June 20, 1978. Utilizing these novel components, we have now discovered a method and circuitry for producing satisfactory celeste effect in all octaves of a digital electronic musical instrument. Additionally, in our co-pending application, Ser. No. 917,296, now U.S. Pat. No. 4,196,651 filed June 20, 1978, we disclose novel detuning circuitry incorporated into the integrated circuit components shown and described in the foregoing Schwartz et al applications, for providing non-redundant generator unlocking. Briefly, and as more fully explained in our aforesaid co-pending application, these circuits comprising novel "pulse dropping" circuitry on each generator chip or integrated circuit component, for providing detuning of the nominal frequencies produced by the tone generator circuits located on that chip or integrated circuit component. This "pulse-dropping" circuitry is specifically designed for solving the problem of "locking" of frequencies in situations where two or more generators located on different chips or integrated circuit components are assigned to the production of the same tones or of harmonics of the same fundamental frequencies. Utilizing these same novel features, together with additional novel external circuitry disclosed herein, we have now discovered how to provide suitable celeste effects and vibrato effects across the entire range of performance in instruments utilizing these novel tone generator chips or integrated circuit components.